The Role of Renewable Natural Gas (RNG)
Renewable Natural Gas (RNG) is poised to play an essential role in helping provide reliable energy to a growing world population while reducing emissions of methane and other substances that cause climate change.
The World Bank forecasts solid waste will increase nearly 70% by 2050, as the world population grows. Landfills are significant sources of methane emissions. An article in Science Advances describes using satellite imagery and analysis to estimate that landfills are the third largest source of methane emissions globally, trailing oil & gas systems and agriculture.
The Coalition for Renewable Natural Gas (RNG Coalition) notes, “Because RNG captures emissions from society’s waste streams and redeems its energy value, it has the lowest lifecycle carbon intensity (CI) of any clean energy source available today. RNG helps decarbonize energy and combats climate change.”
RNG is not just about landfills, it is potentially about all organic wastes. For example, agricultural operations are the second largest source of methane emissions. According to U.S. Dairy, there are approximately 29,000 dairy farms in the United States, supplying humans with nutrient-dense milk and other dairy products. Cows stand at the top of the dairy product stream providing the milk supply, but their manure is a significant source of methane emissions. Collecting the manure into Anaerobic Digesters and capturing the methane it produces as it breaks down creates a potentially lucrative source of biogas.
Simply put, RNG whether it is sourced from landfills or agricultural operations is a win-win for humanity and the environment.
The Problem with Selling Biogas and Landfill Gas
Biogas and landfill gas in their raw states have some of the same problems that affect geologic natural gas produced from oil and gas wells – these raw gas streams typically contain impurities at levels that often exceed pipeline specification. Most commercial pipelines have specifications for contaminants, including oxygen, hydrogen sulfide, carbon dioxide, and other substances, to protect infrastructure and maintain safety.
Before biogas and landfill gas can be added to the gas grid, it must be upgraded or purified into RNG by removing carbon dioxide and other contaminants such as H2S, water, oxygen, and siloxanes to meet pipeline specifications. Hydrogen sulfide (H2S) is one of the most common contaminants of gas sourced from Anaerobic Digesters and Landfills, however, H2S is highly corrosive to metal pipelines, valves, and other equipment. It is critical to keep H2S out of the system to avoid the risk of a catastrophic failure.
As we noted in our article Gas Treating – Processing Solutions for Multiple Industries, The University of Texas found that the interstate pipeline specifications for H2S range between 0.25 grains per 100 cubic feet to 1.0 grains. Natural gas producers must take steps to decontaminate, purify and/or otherwise upgrade their produced gas to meet pipeline specifications.
Gas Treating for Upgrading to RNG
In our article, Gas Sweetening, Sour Gas Treatment Strategies by Volume, we identified the three primary categories of gas treating to remove H2S from landfill gas, biogas and natural gas produced from oil and gas wells:
- Scavengers and Adsorbents
- Catalytic reactions
- Mechanical destruction or Injection into disposal wells
Conventional H2S treatment methods, including scavengers, adsorbents and catalytic reactions are plagued with a variety of downsides:
- Create negative downstream processing effects
- Require the use of chemicals that can be expensive and present a safety risk
- Require the disposal of contaminated media, creating environmental and safety risks
- Operational complexity, requiring frequent oversight on location and problem solving
Liquid Redox Solution for Gas Treating
In our VALKYRIE™ H2S removal system, we have commercialized a Redox (Reduction-Oxidation) process for converting H2S into elemental sulfur using chemistry (Reduction) that can be regenerated and be used again by exposure to air (Oxidation).
The gas (i.e., Methane, CO2, other process gases) containing the H2S exits the system sweet (without H2S) and the elemental sulfur is filtered from the regenerated chemistry where the chemistry is recirculated to perform the reaction again and the sulfur is collected in a container available for reuse or disposal.
The VALKYRIE system utilizes TALON® chemistry, our non-toxic, biodegradable Redox chemistry. In combination with our advanced automation and control technology, we have created “The Next Generation Redox” system.
Benefits of the VALKRYIE gas treating system:
- A green solution that converts H2S into benign substances including water and elemental sulfur
- Universal application for biogas, landfill gas and oil and gas production
- Widest operating envelope of any H2S Treating method extending across the full spectrum of pressures, flow rates and H2S concentrations
- Treating to established specifications for sales pipelines, gas lift and fuel gas
- Flexibility of placement along the production stream whether at the anaerobic digester, at a landfill, wellhead, refinery, in a direct or tail gas treating configuration
- 100% turndown
We specialize in meeting the most stringent outlet specifications.
Citations
World Bank press release, September 20, 2018
EPA Livestock Anaerobic Digester Database
Physics.org, Satellite data finds landfills are methane ‘super emitters’
U.S. Dairy, How Dairy Farmers Are Reducing Methane And Greenhouse Gas Emissions
